1. Field of the Invention
This invention relates to an antibacterial calcium phosphate ceramic and antibacterial calcium carbonate. More particularly, the invention relates to a calcium phosphate ceramic and calcium carbonate made to carry silver and silicon and/or ions thereof or silver, silicon and zinc and/or ions thereof, wherein the calcium phosphate ceramic and calcium carbonate are safe, exhibit a high degree of whiteness and resist discoloration to the maximum extent.
2. Description of the Prior Art
It is known that metals such as silver and zinc as well as ions and salts of these metals exhibit a strong antibacterial property, and various processes have been proposed for utilizing these. However, when these metals are used as is in mixture with a substrate such as resin, fibers or paint, problems arise involving dispersibility with respect to the substrate, the eluting property of the metal ions, tinting and discoloration. For this reason, use in wide fields of application has not been possible.
Substances in which antibacterial metals, metal salts or metal ions are carried on highly safe ceramics such as zeolite, calcium secondary phosphate and hydroxyapatite have recently been proposed as substances which utilize the antibacterial property of the above-mentioned metals. Since these substances exhibit reduced elution of the carried antibacterial metal ions into water and have improved dispersibility with respect to the substrate, they can be utilized comparatively safely and in many fields of application. However, depending upon the medium used, even these substances undergo elution of their metal ions into the medium, and therefore they cannot always be used with complete safety in all types of media. Moreover, it is known that silver generally is sensitive to light and will break down and change color to gray or black when exposed to light. Accordingly, silver salts undergo discoloration when used as is. Antibacterial agents in which this metal salt is carried on ceramics or the like can lead to problems not only in terms of discoloration but also in terms of safety since the elution of silver from the silver salt and the release of silver salt from the ceramics cannot be reasonably prevented.
Though zeolite made to carry silver by means of ion exchange exhibits less discoloration in comparison to those cases where the silver salt is used as is, discoloration with the passage of time is unavoidable. In comparison with zeolite carrying silver, hydroxyapatite made to carry silver by ion exchange is much improved in terms of discoloration attributable to the silver, but complete suppression of discoloration has still not realized, and the degree of whiteness is not to a high degree even before discoloration can occur. In a case where calcium primary phosphate, calcium secondary phosphate or calcium pyrophosphate is used alone as the carrier, there is little improvement with regard to the elution of silver and discoloration.
Studies have been conducted with a view to improving upon the foregoing, and processes for carrying zinc along with silver and for heat-firing have been considered. However, in a case where zinc is carried together with silver, the antibacterial agent tends to become a light gray in color as the amount of silver carried is increased, and even though the color is near white, the degree of whiteness is low. In addition, discoloration cannot be completely suppressed over an extended period of time. In a case where heat-firing is carried out, discoloration can be suppressed. Nevertheless, the antibacterial agent itself still becomes light brown in color and the degree of whiteness diminishes as the amount of silver carried increases. These problems arise when silver is used as the antibacterial metal, and though improvements have been made, they still have not been resolved totally.